How to redirect the output of the time command to a file in Linux?

Just a little question about timing programs on Linux: the time command allows to measure the execution time of a program:

[ed@lbox200 ~]$ time sleep 1

real    0m1.004s
user    0m0.000s
sys     0m0.004s

Which works fine. But if I try to redirect the output to a file, it fails.

[ed@lbox200 ~]$ time sleep 1 > time.txt

real    0m1.004s
user    0m0.001s
sys     0m0.004s

[ed@lbox200 ~]$ cat time.txt 
[ed@lbox200 ~]$ 

I know there are other implementations of time with the option -o to write a file but my question is about the command without those options.

Any suggestions ?

Try

{ time sleep 1 ; } 2> time.txt

which combines the STDERR of "time" and your command into time.txt

Or use

{ time sleep 1 2> sleep.stderr ; } 2> time.txt

which puts STDERR from "sleep" into the file "sleep.stderr" and only STDERR from "time" goes into "time.txt"

Simple. The GNU time utility has an option for that.

But you have to ensure that you are not using your shell's builtin time command, at least the bash builtin does not provide that option! That's why you need to give the full path of the time utility:

/usr/bin/time -o time.txt sleep 1

Wrap time and the command you are timing in a set of brackets.

For example, the following times ls and writes the result of ls and the results of the timing into outfile:

$ (time ls) > outfile 2>&1

Or, if you'd like to separate the output of the command from the captured output from time:

$ (time ls) > ls_results 2> time_results

If you care about the command's error output you can separate them like this while still using the built-in time command.

{ time your_command 2> command.err ; } 2> time.log

or

{ time your_command 2>1 ; } 2> time.log

As you see the command's errors go to a file (since stderr is used for time).

Unfortunately you can't send it to another handle (like 3>&2) since that will not exist anymore outside the {...}

That said, if you can use GNU time, just do what @Tim Ludwinski said.

\time -o time.log command

Since the output of 'time' command is error output, redirect it as standard output would be more intuitive to do further processing.

{ time sleep 1; } 2>&1 |  cat > time.txt